1. Field
The invention relates to monitoring channels in a radio system, particularly in a cognitive radio system.
2. Description of the Related Art
Bands at the radio frequencies of the electromagnetic continuum have already long been too crowded and the distribution of users has not been even in the bands, which has resulted in a poor service. A wireless technology of SDR (Software-Defined Radio) is an attempt to relieve the problems.
Cognitive radio belongs to an SDR platform where a radio automatically searches for an unused channel for its transmission. The transmitter has an adaptive software which does the searching and enables the radio to reconfigure its communication parameters when an unused channel is found. Using the software, the radio starts its operation by performing an LBT (Listen Before Transmission) scheme for a free channel. The radio may also jump from a channel, whose quality of service may be deteriorating, to a new channel lightning fast without causing an interruption in its transmission.
However, searching for an available channel has proved a difficult problem. The problem is particularly complicated when a radio has a large number of channels to sift through and among them (only) a few channels may be free. The searching takes a long time and the result is not reliable but ends up in a channel which is actually in use already. Hence, there is a need for a fast and reliable search process.